The present application is in the field of plant developmental biology and relates to methods for altering the rate at which a plant develops using molecular genetic techniques.
Plant genomes contain relatively large amounts of the modified nucleotide 5-methylcytosine (5mC) (Y. Greenbaum, et al., Nature 292: 850 (1981)). Despite evidence implicating cytosine methylation in plant epigenetic phenomena, such as repeat-induced gene silencing (TIGS), cosuppression, and inactivation of transposable elements (F. F. Assaad, et al., Plant Mol. Biol. 22: 1,057 (1993); C. Napoli, et al., Plant Cell 2: 279 (1990); J. Bender et al., Cell 83: 725 (1995); P. S. Chomet, et al., Genetics 138: 213 (1994); R. A. Martienssen, et al., Curr. Opin. Genet. Dev. 5: 234 (1995); M. A. Matzke, et al., Plant Physol., 107: 679-685 (1995)), the role of cytosine methylation in plant developmental processes is not clear.
In Arabidopsis, ddm mutants (decrease in DNA methylation) have been isolated with reduced levels of cytosine methylation in repetitive DNA sequences, although these mutations do not result in any detectable change in DNA methyltransferase enzymatic activity (A. Vongs, et al., Science, 260: 1,926 (1993), T. Kakutani, etal., Nucleic Acids Res. 23: 130 (1995)). After several generations of self-pollination, ddm mutants exhibit a slight delay (1.7 days) in flowering, altered leaf shape, and an increase in cauline leaf number (T. Kakutani, et al. (1995)).
The exact mechanisms that mediate plant development are presently not well understood. Plants that have an increased rate of development would be highly useful in plant breeding programs. Specifically, numerous plants, such as tree species, have extremely long generation times and therefore the number of crosses that can be generated within a given year or plant cycle is limited. In one extreme case, certain species of bamboo flower only once every one hundred years. Methods which could be used to decrease the maturation time would be highly beneficial in breeding programs involving many plants.
A reduction in the rate a plant matures can be used to increase the biomass production of a given plant. For numerous plants, increases in biomass yields would increase the economic value of the commercial plant. For example, flax, tobacco, alfalfa, spinach, lettuce, etc.
It is therefore the focus of the present invention to provide methods for increasing or decreasing the time required for a plant to mature as well as plants which are produced by these methods.
All references discolosed throughout this application are hereby incorporated by reference in their entirety.
The present invention is based on the unexpected observation that a decrease of about 70% in the amount of methylated DNA present in a plant genome results in a plant that requires more time to mature while an increase in the amount of methylated DNA present in a plant genome results in a plant that requires less time to mature. Based on these observations the present invention provides methods of altering a plant, plant cells, plant tissues or plant seeds, so as to obtain a plant that has an altered rate of maturation. In one method, the rate of maturation is increased by altering the plant, plant cells, plant tissues or plant seeds, using molecular techniques, such that the plant has a sufficient increase in methylated DNA so as to yield a plant that matures faster than a non-altered plant. In another embodiment, the rate of maturation is decreased by altering a plant, plant cells, plant tissues or plant seeds, using molecular techniques, such that the plant has a sufficient decrease in methylated DNA so as to yield a plant that matures slower than a non-altered plant.
The present invention further provides plants that have an altered rate of maturation that have been produced using the methods herein described.